A Thin Film Transistor Liquid Crystal Display (briefly called as TFT-LCD) has characteristics of small volume, low power consumption, being free of radiation, etc., and plays a leading role in the current market for flat panel displays.
In recent years, the TFT-LCD has been developed rapidly, its size and resolution have been increased continually, and a liquid crystal television of large size and high resolution has become a mainstream of TFT-LCD development. With continual increasing of the size of the TFT-LCD and continual enhancement of its revolution, it is required that a driving circuit with a higher frequency is used in order to improve the display quality, and it is very hard for the mobility of existing amorphous silicon thin film transistors to meet requirements of the liquid crystal display. The mobility of amorphous silicon thin film transistors is generally about 0.5 cm2/V·S, but a mobility of 1 cm2/V·S or above is needed when the size of the liquid crystal display exceeds 80 inches and its driving frequency is 120 Hz. Obviously, it is very hard for the mobility of existing amorphous silicon thin film transistors to meet this. A metal oxide TFT (amorphous IGZO) has a high mobility, a good uniformity and transparency, and its manufacturing process is simple. It can meet the demands of large-size liquid crystal displays and active organic electroluminescence better, and arouses more attention.
However, upon fabrication of the metal oxide TFT in prior art, a protective layer is generally added over a metal oxide, so as to avoid the metal oxide layer from being destroyed when source and drain metal electrodes are formed. As such, the number of patterning processes is increased, and the production efficiency is affected.